Many compositions and many processes exist for the dyeing of keratin fibers, and in particular human hair.
Thus, it is known practice to dye keratin fibers, in particular human hair, with dye compositions containing oxidation dye precursors, in particular ortho- or para-phenylenediamines, ortho- or para-aminophenols, and heterocyclic compounds, such as diaminopyrazole derivatives, which are generally known as “oxidation bases”. Oxidation dye precursors, or oxidation bases, are colorless or weakly colored compounds, which, when combined with oxidizing products, can give rise to colored compounds and dyes via a process of oxidative condensation.
It is also known that the shades obtained with these oxidation bases can be varied by combining them with couplers or coloration modifiers, the latter being chosen especially from aromatic meta-diamines, meta-aminophenols, meta-diphenols and certain heterocyclic compounds.
The variety of molecules used as oxidation bases, on the one hand, and as couplers, on the other hand, allows a wide range of colors to be obtained.
The “permanent” coloration obtained by means of these oxidation dyes should moreover satisfy a certain number of requirements. Thus, it should have no toxicological drawbacks, it should allow shades to be obtained in the desired intensity, and it should show good resistance to external agents such as light, bad weather, washing, permanent-waving, perspiration and rubbing.
The dyes should also allow gray hair to be covered and, finally, they should be as unselective as possible, i.e. they should allow only the smallest possible color differences along the same keratin fiber, which may indeed be differently sensitized, i.e. damaged, between its end and its root.
In conclusion, it turns out that although standard base-coupler combinations allow a wide range of colors to be obtained, they do not satisfy the criteria mentioned above and, especially, they often lead to the generation in the fiber of varied coupling products that pose fastness problems that are difficult to control, for instance selective changing of the color.
Another way of dyeing keratin fibers, in particular the hair, is to use direct dyes.
The standard dyes that are used are, in particular, dyes of the nitrobenzene, anthraquinone, nitropyridine, azo, cationic azo, xanthene, acridine, azine or triarylmethane type, or natural dyes.
These dyes, which are colored and coloring molecules with affinity for the fibers, are applied to the keratin fibers for a time required to obtain the desired coloration, and are then rinsed out.
Direct dyeing is consequently very widespread in practice since it also presents certain advantages over oxidation dye precursors and, especially, often presents better harmlessness and absence of sensitization of the hair caused by the oxidative process.
However, the colorations obtained are temporary or semipermanent, since the nature of the interactions that bind the direct dyes to the keratin fiber, and their desorption from the surface and/or core of the fiber, are responsible for their weak dyeing power and their poor fastness with respect to washing, bad weather or perspiration. These direct dyes are also generally light-sensitive as a result of the poor resistance of the chromophore to photochemical attack, and lead over time to fading of the coloration of the hair.
There is thus a need for a composition for dyeing keratin fibers, in particular human keratin fibers and more particularly the hair, which is harmless, totally compatible with keratin fibers and sparingly selective, which gives a wide variety of colors, is powerful, and also makes it possible to obtain fast, stable coloration of keratin fibers, which shows resistance to external agents, such as light, bad weather, washing, perspiration and rubbing, and to subsequent treatments, such as permanent-waving.
There is also a need for a dye composition that allows the treatment of all kinds of keratin fiber and of all hair types, for example gray hair, even if this hair has undergone a treatment beforehand, such as a bleaching or permanent-waving treatment.
Finally, there is a need for a composition that achieves the dyeing without it being necessary to sensitize the keratin fiber or the hair beforehand.